Material deposition is widely used in window glass coating, flat panel display manufacturing, coating on flexible films (such as webs), hard disk coating, industrial surface coating, semiconductor wafer processing, photovoltaic panels, and other applications. Materials are sputtered or vaporized from a target source and deposited on a substrate. Conventional deposition systems have various drawbacks in material utilization. For example, referring to FIGS. 1A-1E, a deposition system 100 includes a rectangular target 110 over a large substrate 115 in a vacuum chamber 120. A magnetron 130 is held stationary behind the target 110. The substrate 115 can be transported in a direction 150 relative to the target 110 and the magnetron 130 such that the substrate 115 can receive a uniform deposition across its top surface. The deposition system 100 can also include a power supply 140 that can produce an electric bias between the target and walls of the vacuum chamber 120.
The magnetron 130 includes a magnetic pole 132 of a first polarity and a magnetic pole 135 of a second polarity opposite to the first polarity. The magnetron 130 can produce magnetic flux outside of the sputtering surface 112 on the lower side of the target 110 (as shown in FIG. 1B) to confine electrons near the sputtering surface 112. More electrons can be confined near the magnetic field parallel to the sputtering surface 112 wherein the magnetic field strength is at local maximum. A close loop can be formed by the locations having local maximum magnetic field strength. The close path can guide the migration path for the trapped electrons near the sputtering surface 112. The closed-loop magnetic field can enhance the ionization efficiency of the sputtering gas (i.e. the plasma) to produce more effectively confine electrons near the sputtering surface 112. The enhanced ionization can also lower the operating pressure during sputter deposition.
A drawback of the deposition system 100 is the uneven erosion in the target 110 after repeated sputtering operations. As shown in FIGS. 1D and 1E, a non-uniform erosion pattern 115 usually appears over the sputtering surface 112 of the target 110 after a period of sputtering operations. The erosion pattern 115 can include a close-looped groove that matches the magnetic field strength. The target locations 116 experiencing the most erosion correspond to locations having high magnetic field strength where the sputtering gas is the most enhanced. The target 110 has to be replaced once the target locations 116 reach near to the top surface of the target 110. The unused target material 117 is discarded. The non-uniform erosion therefore causes low target utilization in the target 110 in the deposition system 100.
There is therefore a need to maximize the utilization of target materials and to minimize waste in material depositions.